You can get the .bind event namespace via event.handleObj.namespace, …

…but what about the .trigger namespace? I propose event.namespace.

src/event.js

@@ -368,7 +368,7 @@ jQuery.event = {
 	},
 
 	handle: function( event ) {
-		var all, handlers, namespaces, namespace, events;
+		var all, handlers, namespaces, namespace_sort, namespace_re, events;
 
 		event = arguments[0] = jQuery.event.fix( event || window.event );
 		event.currentTarget = this;
@@ -379,7 +379,8 @@ jQuery.event = {
 		if ( !all ) {
 			namespaces = event.type.split(".");
 			event.type = namespaces.shift();
-			namespace = new RegExp("(^|\\.)" + namespaces.slice(0).sort().join("\\.(?:.*\\.)?") + "(\\.|$)");
+			namespace_sort = namespaces.slice(0).sort();
+			namespace_re = new RegExp("(^|\\.)" + namespace_sort.join("\\.(?:.*\\.)?") + "(\\.|$)");
 		}
 
 		events = jQuery.data(this, "events");
@@ -393,12 +394,13 @@ jQuery.event = {
 				var handleObj = handlers[ j ];
 
 				// Filter the functions by class
-				if ( all || namespace.test( handleObj.namespace ) ) {
+				if ( all || namespace_re.test( handleObj.namespace ) ) {
 					// Pass in a reference to the handler function itself
 					// So that we can later remove it
 					event.handler = handleObj.handler;
 					event.data = handleObj.data;
 					event.handleObj = handleObj;
+					event.namespace = all ? '' : namespace_sort.join(".");
 
 					var ret = handleObj.handler.apply( this, arguments );